While maturing, T cells undergo a massive, largely random rearrangement of their T cell receptor (TCR) genes, resulting in a near unique antigen specificity for each T cell in the body. When a pathogen such as HIV-1 enters the body, T cells recognizing HIV-1 antigens are expanded and a select number of these T cells become overrepresented or immunodominant. However, the ability of these immunodominant HIV-1 specific CD8 T cells to control HIV-1 replication varies considerably amongst individuals, and these differences play a major role in determining the rate of disease progression. Individuals able to mount multiple responses targeting HIVGAG have reduced viral loads. Of note, a majority of elite controllers express HLA-B alleles associated with potent anti-HIVGAG responses, suggesting that in rare cases effective CD8 T cell responses can control HIV-1 infection. However, not all T cell responses targeting HIVGAG are protective and there is no consensus on why this is. Providing insight into why one HIV-1 specific T cell response is more effective than another is a major goal of this project. One way to determine whether one T cell is able to function better than another is to perform population studies in which the presence of a particular T cell response is correlated with viral load. While informative, these studies do not shed light onto why one response is better than another. In vitro studies using HIV-1 specific T cells isolated from individuals indicate that T cells with a higher functional avidity function to control HIV-1 infection better than those with a lower functional avidity, though region of HIV-1 targeted also is important. However, there are several confounding factors including the differentiation state of the T cells and the expression of costimulatory and adhesion molecules that preclude direct correlations of functional avidity and TCR affinity. In this application we propose model systems that will permit direct comparison of various HIV-1 specific TCRs and functional avidity through unique proprietary approaches to increase the affinity of natural HlV-specific TCRs and test such responses in vitro and in vivo.